1. Field of the Invention
The present invention relates to a lock-up clutch installed on a hydraulic torque conventor or a fluid coupling.
2. Description of the Prior Art
Hitherto, vibration damper which absorbs the torsional vibration from the prime mover has been installed in lock-up clutch for a hydraulic unit. Said vibration damper was installed conventionally on a hydraulic unit or near the small caliber of a fluid circulation passage of a fluid coupling or in the outside of a fluid circulation passage near a stator as is disclosed in U.S. Pat. Nos. 4,027,757, 4,049,093 and so on, so that the dimension in the axial direction of a hydraulic unit or a fluid coupling was remarkably enlarged, being disadvantageous in the loading of a vehicle. Moreover, the piston controlling the operation of said lock-up clutch, slides on the driving function, for example, spline, slot, of power transmission in an axial direction to a turbine runner in said conventional lock-up clutch so that remarkable unreasonableness existed because of the frictional resistance generated at the contact surface of the driving function of power transmission at the release of a lock-up clutch, so that the reliability was made low.